Generator Operation

[Pete]

It has been my observation that most boat owners when anchored, run their generators for a number of hours and then shut them down. When I have inquired as to why they cycle the units, the most common answer is to give the generator a rest. Ignoring for the moment the noise, fuel use, exhaust, and additional hours on the unit, my question is does this help or hurt the generator. Once a diesel reaches a stable operating condition, I would think it is much better for the unit to continue to run, to avoid the temperature shifts associated with on/off cycling. Am I missing something?

Pete

 

[Boatsb]

In a perfect world 2 generators switching at 8 hour shifts would be great. I barely have room for the one I have. Therefore I run it when I need it. Fuel is not the issue as much as maintenance to me as it burns well below 1 gal/hour. Time to change the oil and tighten the belts is harder to find lately.

Once it gets to operating temp and runs the expansion is completed and contraction as it cools is a small issue unless you run it an hour and the shut it for one repeatedly.

 

[Pascal]

i dont' think gennies need a rest...

I prefer not to run mine unless i need to (AC, cooking, charging) but that's for noise, fuel usage and hours... Somethign we dont' have to deal with when on inverter

 

[MikeP]

Depends oh how you operate - if you go somewhere and anchor for a couple of days or longer, you of course need to run the genny for several hours a day to charge the batts. We don't ever worry about running the genny as far as genny wear. It will last a lot longer than the boat engines will and likely a lot longer than our boating life.

We tend to not run the genny except to charge the batteries as necessary because the inverter can handle everything we need to run except ac/hot water. So the charging time for the batts is also perfect for heating hot water.

If we need the ac than the genny is running for as long as it needs to run. THe longest trip we have done in the boat was 10 days and for that trip, on LI sound in the summer, the genny ran for the entire 10 days because we wanted the ac.

Right now, anchored at St Michaels in the Chesapeake bay, we are running the genny only to keep the batts charged - about 3 hours/day.

I'm on the internet courtesy of somebody's wireless that's "bleeding" coverage into the harbor!

 

[krush]

They don't need a rest, but cycling them once a day isn't going to hurt anything either.

If there is no need to run the thing they one is wasting fuel and putting wear on equipment.

We start our cars up and shut them off quite a bit....

 

[yachtbrokerguy]

I showed a boat last week, it had two Northern Lights generators. One of the gennies had 11,000 hours and the other had 12,000 hours. A typical buyer of course would be concerned about so many hours, but they run just fine with no smoke. Not worth replacing things that are not broken.

What is the oldest generator of readers here? It seems to me that replacing the exhaust riser is the most common required maintenance/repair, what other problems have you had?

 

[doc g]

THe NL people told me they had a 20 KW that was replaced due to a rear main seal leak . It had over 20,000 hours when thay pulled it apart it still had crosshatch in the cylinders . Those liners are replaceable also, I don't think you run them too much as long as you keep a good load on them.......Pat

 

[34Hatt]

They don't need a rest, but cycling them once a day isn't going to hurt anything either.

If there is no need to run the thing they one is wasting fuel and putting wear on equipment.

We start our cars up and shut them off quite a bit....

Plus if there is no load that is not good for them. Which means if you don't have AC going eventually everything will be satisfied and your just wasting fuel. Plus when on the hook I love the Quiet

 

[Nonchalant1]

I showed a boat last week, it had two Northern Lights generators. One of the gennies had 11,000 hours and the other had 12,000 hours. A typical buyer of course would be concerned about so many hours, but they run just fine with no smoke. Not worth replacing things that are not broken.

What is the oldest generator of readers here? It seems to me that replacing the exhaust riser is the most common required maintenance/repair, what other problems have you had?

Mine is 30 years old (original Onan 15KW) on 1978 53MY. I'll bet there are plenty of older gennys out there still running.

 

[ThirdHatt]

I agree, genny's do not need a rest until they need service. They are designed to be run nonstop, so when you want power run 'em and forget 'em!

I have two, a 16kw NL and a 7.6kw Westerbeke. The little Westerbeke runs pretty much the entire boat and only burns 1/2 gallon of fuel per hour loaded. This is the preferred genset due to light fuel burn (compared to up to 1.5gal/hr for the NL!) and 1/2 the replacement cost of the 16kw NL.

When on the hook for extended periods, I run the 7.6kw for 4 days (~100hrs) and then swap to the 16kw while I change the oil and check/change it's racor on the 7.6kw. This is the day we wash clothes, do any heavy cooking, etc while we have so much power to use. Then I go back to the 7.6kw for four more days and so on. This way I use much less fuel and reduce the time/wear on the 16kw. Although I service the 7.6kw every 5th day, the NL goes 20 days before needing it's 100hr service because I only run it one day out of five. If I had two identical sized gens like most boats with two, I would simply alternate every 4 days from one to the other to allow for servicing.

A boat that I am a guest on frequently has two large identical NL gensets installed new in 2002 and have right at 8,000hrs each at last check with no problems whatsoever form either. They alternate every 6 days, or 150hrs between servicing and they run heavily loaded at all times. These are the kinds of reports that give NL such a great reputation.

 

[Passages]

I installed a 400w inverter to run TV, Stereo, and small electric loads. This avoided having to fire up the genny if the kids only want to watch TV while underway.

I would run the genny a few hours a day while at anchor to handle major loads such as the hot water heater, AC, Refrig or stove.

When connected to shore power, I would run the genny loaded 1x weekly for about 15 minutes to get it up to temp, circulate lube oil and blow out any cobwebs. (Check discharge water flow, loaded output, battery status & general function)

A weekly cycle of your mains is also a good idea. The trick is to get them up to operating temp which may be tough if you are tied to the dock.

 

[krush]

When on the hook for extended periods, I run the 7.6kw for 4 days (~100hrs) and then swap to the 16kw while I change the oil and check/change it's racor on the 7.6kw.

If i was running a gen 24/7, I'd extend that oil change to much longer. Run synthetic and if you want, get a bypass filter.

Hell, even without synthetic I'd go at least 200-300 hours if it was running non stop (and possibly longer).

But that is just me LOL

You should take oil samples and see how much life is left at 100 hours.

 

[smoothmove]

My MCCK (gas) gen is 40 years old. It's smokes a bit, wheezes now and then, sputters occasionally, and is starting to drool a little (oil), but it always starts and cuts loose the juice. That's about as good as most people over 40 can claim. Have to admit I'm always pleased and maybe a little surprised when it answers the call.

Eric

 

[Ross Macdonald]

We have mirror image 15KW Onan MDL3 gensets. We just returned from 66 days sitting on the hook. Our daily usage is to run one gen 3 hrs. in the morning for battery charge, cooking, shower, etc. Then sit on the 4KW inverter until about 7 in the evening and run 3 hours for the same reasons. This keeps the hrs. on the gens even. When we are on a trip like this I also leave the block heaters on so any time the gens are on there is a load on them even if all other loads are finished and some additional battery charging needs to be completed. I realize this is West Coast usage where we don't have to run AC. I usually turn on all AC units once a week just to exercise them. Our gensets were installed in 1993 and now have 3900 hrs. on each. I agree with a longer oil change interval if you have alot of usage. We check oil every morning and after about 200 hrs. on each genset on this trip, the oil level was still at the line. By the way, we just looked at a larger yachtfisher that had twin 25 KW Northern Lights and they had 19,000 hrs each on the meters. Having seen some of the megayachts come in here, they run gens 24/7 and hardly ever plug in. Probably because most shorepower is inadequate for all of their power needs. Just my 2 cents....

 

[ThirdHatt]

If i was running a gen 24/7, I'd extend that oil change to much longer. Run synthetic and if you want, get a bypass filter.

Hell, even without synthetic I'd go at least 200-300 hours if it was running non stop (and possibly longer).

But that is just me LOL

You should take oil samples and see how much life is left at 100 hours.

Very good point Krush, thanks for the advice. I just always heard to change it every 100hrs, and I try to stick close to that. I have run 5 and 6 days straight before just being lazy, but I try to shorten the next interval. It probably is overkill, but oil and filters are (relatively) cheap so I try to stick to the schedule. The small gen only holds a gallon of oil so that with the filter is under $20 for the service. The oil just begins to darken by the time I change it usually. I have never done oil samples, so I probably should and see what's really going on.

I just worry about the engine longevity because that is the expensive part of the genset. Complete armatures are $1500, so the electrical side is of comparatively little concern when it comes to replacing parts.

Here in the deep south we have to run the A/C for 9 months of the year and the heat for one to two months, so the gensets in this region get a workout. One day I'll install an inverter for that month or two when it is nice enough to let the outside air in. In the mean time, I still run the gen to keep the fridge and icemakers going and I have been known to run one unit on heat and the other unit on A/C in the salon to balance temps and keep a load on the gen!

 

[Boatsb]

Shortening the next interval is of no value except mentally. I thought about that too with the car. When I ran over I would thing OK the next time I will change it 2500 miles. Truth is new oil and filters will take the same time to break down and get dirty no matter how long the old was there.

I have spoken to others about this too. The caveat is getting all the old oil out and keeping the engine clean. If there is buildup all bets are off.

 

[ThirdHatt]

Scott I agree with you, I just like to keep the services close to when the hour meters are at whatever hundreth. It's just easier that way.

 

[Brian Degulis]

Commercial boats (tugs etc) almost always have block heaters. When they're shut down the block heaters are on even in the summer. So the temps never get below around 150 degrees. You would be amazed how much this extends oil life proven by analysis. Eliminating the hot cold cycles helps a lot you see fewer gasket and seal failures also.

Gens are always run under moderate load even if you have to create it they try never to run lightly loaded. In the early 80s a whole bunch of 20KW 271 3 phase gen sets came on the market. These were rail road units used for refridgerated cars. They would start these things and they would run un attended for days or weeks. But they were oversized and properly loaded most had over 10,000 hours some 20 or more and most were still in great shape with lots of service life left.

Our boats the mains and gens suffer more from lack of use than wear. But what can you really do about it if you just let the gen run it will often be running so lightly loaded that in itself will hurt it. If you go the block heater route your electric bill will be very high.

Brian

 

[luckydave215]

I too have mirror image Onans, but in 20kw. Underway we run one 8 hours, then the guy coming on watch checks the vitals of the other gen, fires it up and switches over. This equalizes the hours, insures the vital signs of the generators get checked at regular intervals, and can go on for ever if need be. One of my friends (big time tournament captain) lived on a 60c back in the eighties for three years traveling the circuit, and they ran the gens in this fashion the whole time...(8 on/8 off)... without a single problem. Of course, they started with a brand new boat! (drool.....)
On the hook, we can "dry camp" for 18 hours on the inverter if we don't need ac or the stove (or a shower)
I usually turn on a bunch of stuff I really don't need to create load such as lights, watermaker, one heater fighting with the adjacent ac, bait tank, etc. to create enoough load for the (too big in my opinion) 20kw sets.

 

[ThirdHatt]

LuckyDave, If I may ask why 8 hr intervals? That seems like alot of un-necessary heat cycles and of no advantage that I can see. Why not run them for however long you need them up to what your service interval is? I currently use 100hrs, so I run for ~100hrs and then swap gens. If I stop using the gen I just pick up where I left off and continue the cycle. This keeps the hours equal as well as your 8 hr intervals with many less heat cycles and MUCH less starter wear. Surely you have mechanical guages for water temp and oil pressure in addition to safety shutdowns for each, so 100hr intervals should be a non-issue with respect to fluid checks. Maybe it's just how you like to run yours and of course that's great but I wonder if there is something that I missing here? THANKS!